Role of Plant Defence Enzymes in Combating Fungal Infections: A Review

Abstract

Fungal pathogens are responsible for some of the most significant losses in global crop production. Plants exist in environments where constant exposure to potential microbial invaders is unavoidable. Fungal pathogens pose a serious threat to global crop productivity, accounting for significant yield losses and affecting food security across diverse agricultural systems. Plants, being immobile, have evolved complex defence mechanisms to recognise and counteract fungal attacks. Natural resistance mechanisms can be leveraged to develop sustainable, enzyme-based strategies for controlling fungal diseases in agriculture. Among these, the activation and regulation of defence-related enzymes represent a vital aspect of both innate and induced immunity. These enzymes, including chitinases, β-1,3-glucanases, peroxidases, polyphenol oxidases, phenylalanine ammonia-lyase (PAL), and lipoxygenases (LOX), serve multiple roles such as degradation of fungal cell walls, reinforcement of host structural barriers, detoxification of pathogen-derived toxins, and biosynthesis of antimicrobial secondary metabolites. Their expression is controlled through intricate signalling pathways involving salicylic acid, jasmonic acid, and ethylene, as well as transcription factors like WRKY and MYB, and epigenetic regulators including small RNAs and histone modifications. Recent advances in plant biotechnology have expanded the capacity to enhance these enzymatic defences through transgenic approaches, genome editing technologies like CRISPR/Cas, and the use of natural or synthetic elicitors that prime plant immunity. Transgenic crops expressing defence enzymes have demonstrated improved resistance to a wide range of fungal pathogens, while gene editing offers precision in modifying key resistance loci without introducing foreign DNA. Despite these advancements, several challenges persist, including the complexity of signalling networks, the trade-off between defence and growth, environmental variability affecting enzyme expression, and the limited understanding of long-term field-level efficacy. Omics technologies, encompassing genomics, transcriptomics, proteomics, and metabolomics, provide powerful tools to dissect enzyme regulation and develop holistic resistance strategies. The multifaceted roles of plant defence enzymes in fungal resistance, their regulatory mechanisms, biotechnological applications, and the future prospects for integrating enzyme-based resistance into sustainable crop protection frameworks. Enhancing endogenous enzyme-mediated defences offers a promising, environmentally responsible approach for managing fungal diseases in agriculture. Strengthening these natural defence mechanisms is key to reducing reliance on chemical fungicides and improving crop resilience under pathogen pressure.